Blood coagulation, clot formation and hemostasis involve a complex multi-step system. Two biochemical pathways, referred to as the intrinsic pathway and the extrinsic pathway are involved in the complex system. In conjunction, the two pathways, each involving numerous protein factors, play a major roll in the control of blood clot formation.
Typically, initiation of blood clot formation is triggered by injury. A series or ‘cascade’ of events which activate various protein factors involved in the two pathways leads to the formation of fibrin from the precursor fibrinogen. Fibrin crosslink formation and interaction with blood platelets which have become activated due to the injury event, form a clot or “insoluble fibrin”, which comprises aggregated platelets and interwoven fibrin.
Where certain factors or events involved in the coagulation cascade are inhibited or blocked, blood clot formation can be impaired leading to prolonged bleeding times. A number of medical conditions related to prolonged bleeding times have been shown to be associated with impairment of cascade events. Impairment can be due to an insufficiency, absence or overabundance of an otherwise normal coagulation factor, can be due the presence of one or more factors having decreased or no activity, or due to the effect or interference of medications or other agents.
A variety of tests have been developed to measure coagulation efficiency. An in vivo test known as the bleeding time test, has been used extensively. The bleeding time test involves forming small cuts on a patients arm and measuring the time it takes for the bleeding to stop. Due to numerous non-uniformities, such as incision direction, depth and length, and large potential for operator inconsistencies, the bleeding time test is often imprecise or inaccurate. The bleeding time test can also cause scarring and is not conducive to monitoring a blood condition over long periods of time.
In vitro tests have been developed that can provide information about certain general aspects of the coagulation cascade. One such test is the prothrombin time (PT) which measures the extrinsic pathway. Another is the partial thromboplastin time (PTT) tests the intrinsic pathway.
Additional test methods have been developed that study platelet aggregation. These tests typically utilize one or more aggregation inducing or enhancing agent (e.g. ADP, collagen, epinephrine and ristocetin) to study the ability of platelets to aggregate. However, since the ability of platelets to aggregate is only one aspect of clot formation, platelets studies, provide limited information regarding physiological clot formation. Similarly, platelet adhesion tests, which measure the ability of platelets to adhere to foreign materials such as glass, also provide limited information, can be very inconclusive and can produce unpredictable results.
It would be advantageous to develop in vitro hemostasis testing that more accurately simulates events at the site of a wound. It would additionally be advantageous to develop tests for detecting insufficiencies related to specific clotting factors and/or platelet factors.